Electronic warfare systems are used on modern military aircraft as part of their offensive and defensive capabilities. These electronic warfare systems emit RF (radio frequency) signals that travel through space. Radar systems use RF emissions to locate and track opposing aircraft and some radar systems are incorporated within missiles to assist in the self-guided propulsion of a missile to its target. An electronic warfare search receiver is used defensively to detect those RF emissions. The receiver searches the range of frequencies (the RF spectrum) in which the RF emissions are likely to occur..The receiver then detects and analyzes the nature of the RF signals. By determining the characteristics of the signals received, the defender will know the nature of the threat and, for example, will know if a radar guided missile has "locked on" to the defender's aircraft. These systems are used in friendly as well as unfriendly aircraft. In a tactical or strategic environment, the number of aircraft and the density and diversity of the emissions in the RF spectrum is quite large and is expected to increase. Existing detection and monitoring equipment that use wide band search receivers will find the RF emissions difficult or impossible to successfully monitor in such an environment. For example, some existing wide band receiver designs employ a threshold detector that requires the incoming signal to attain a certain amplitude before it is recognized as a true signal apart from the ordinary RF background noise. These receivers are incapable of differentiating between high amplitude short duration and low amplitude longer duration pulses when they are first detected. With the existing designs, it is entirely possible that a first RF pulse received will effectively prevent detection of a second RF pulse, from another emitter, during the presence of the first pulse. The first emission source may be identified but the second source is, in effect, masked. Also, in a multiple channel receiver or a channelized receiver, quite frequently there is spill-over energy between the channels. Therefore, multiple pulses may be detected when in fact there is only one emission source. Also, in a spatial domain, when using a four quadrant receiver, a signal coming from one direction may be detected in the other three receiver quadrants and reported as additional signals when in fact there is only one signal from one source.
It is unlikely that a single receiver type will be capable of meeting all offensive or defensive threat detection and analysis requirements dictated by the future electronic warfare environment. Instead a set of search and analysis receivers of complimentary capabilities are likely to be required to meet future demands. Trade offs between probability of intercept, bandwidth, simultaneous signal resolution, sensitivity, receiver complexity and power consumption are necessary. Discriminating between high amplitude short duration pulses and lower amplitude longer duration pulses is an important ability for a modern channelized receiver. It is also important to eliminate any signal detections that occur because of spill-over energy either in the spatial domain or the frequency domain which could cause a single signal to be reported more than once. Reporting one signal three or four times causes confusion and does not accurately reflect the true source of the emission. It would be advantageous to have the ability to detect and differentiate between high amplitude short duration pulses and lower amplitude longer duration pulses and at the same time reject signal detections caused by rabbit ears and backlobe emissions that occur respectively in the frequency and spatial domains.